Method for stabilizing oxide-semiconductor interface by using group 5 element and stabilized semiconductor

ABSTRACT

The present invention provides a method for stabilizing an oxide-semiconductor interface, which is free from the formation of an interface layer (reactive layer) between a semiconductor and an interface oxide and which thereby allows satisfactory exhibition of performance capabilities of a functional oxide and achievement of the stability of oxide-semiconductor interface, yet independent of temperature; it also provides a stabilized semiconductor.

TECHNICAL FIELD

The present invention relates to a method for stabilizing anoxide-semiconductor interface by using a Group Vb element and to astabilized semiconductor. In further detail, the invention of thepresent application provides a method for stabilizing anoxide-semiconductor interface and a stabilized semiconductor, which areuseful in highly integrated circuits, ferroelectric materials,ferroelectric memories, etc.

BACKGROUND ART

Extensive research and development have been made heretofore onrealizing integrated circuits (referred to sometimes hereinafter as“ICs”) with yet higher degree of integration and on realizingferroelectric ICs. As a means of implementing such ICs with higherintegration and ferroelectric ICs, there is established a methodcomprising forming an oxide film on the surface of a semiconductor suchas a silicon to obtain a semiconductor oxide film.

However, the interface between the semiconductor and the oxide film thusformed by a conventional method is extremely unstable, and hence,various reactions were found to occur as to result in unavoidableproblems such as an increase in leak current, a malfunction ofcapacitors, etc.

The problem of such an unstable oxide/semiconductor interface not onlyconcerns the conventionally known electronic components, but also is asevere problem on realizing ferroelectric memories that are attractingmuch attention as an ultimate memory structure in near future. Nosolution of overcoming such an unstable oxide/semiconductor interface isfound to present, and this has been the obstacle in implementing aferroelectric memory. Very recently, however, some methods ofstabilizing the oxide/semiconductor interface are being proposed tosolve the problem of unstable oxide/semiconductor interface.

Such proposals include, for instance, as shown in FIG. 3, a method forstabilizing the oxide/semiconductor interface, which comprisesinterposing a stable interface oxide (50) such as Y₂O₃, MgO, BiSiO₃,etc., between a functional oxide (1) such as BaTiO₃ or SrTiO₃, etc., andthe semiconductor (2) such as a Si substrate.

However, in the case of a known method for stabilizing theoxide/semiconductor interface as shown in FIG. 3, an interface layer (areaction layer) (51), although being thin, was found to be formedbetween the semiconductor (2) and the interface oxide (50), whichunavoidably resulted in a semiconductor with impaired function.

Furthermore, since two types of oxides, namely, the functional oxide (1)and the interface oxide (50), are laminated, there was found anothersevere problem of causing insufficient exhibition of the intrinsicperformance of the functional oxide (1).

Considering the stabilization behavior of the oxide/semiconductorinterface in atomic level, the stabilization is realized by the bondingthat is formed between the elements constituting the interface oxide(50) and the dangling bonds of the elements constituting thesemiconductor (2). For instance, FIG. 4(A) shows schematically a part ofthe structure of a clean (001) surface of semiconductor Si that ishighly reactive, because the outermost surface of the semiconductor Siconsists of Si dimers having dangling bonds that are filled with twoelectrons and those having no electrons. Hence, an interface layer isformed between the semiconductor and the interface oxide as a result.

Furthermore referring to FIG. 4(B), on considering the bonding betweenthe Si dimers (53) in the outermost layer and the Si atoms (52) in thelower layers in the atomic level, it can be understood that the bond ishighly stressed by the strain applied thereto. Thus, if seen in atomiclevel, the bonding between the Si dimers (53) in the outermost layer andthe Si atoms (52) in the lower layers easily causes breakage at lowtemperatures. Hence, theoretically, the oxide/semiconductor interfacecan be stabilized at super low temperatures. In practice, however, thestabilization of the oxide/semiconductor interface was found to beextremely difficult.

Conclusively, no methods capable of stabilizing the oxide/semiconductorinterface independent to temperature while sufficiently exhibiting theperformance of the functional oxide without allowing the formation of aninterface layer (reaction layer) between a semiconductor and theinterface oxide, nor a stabilized semiconductor, are realized topresent.

In the light of the aforementioned circumstances, an object of theinvention of the present application is to provide a method ofstabilizing the oxide/semiconductor interface independent totemperature, which yet sufficiently realizes the performance of thefunctional oxide without forming an interface layer (reaction layer)between a semiconductor and the interface oxide, and to provide astabilized semiconductor.

DISCLOSURE OF INVENTION

As a means of overcoming the aforementioned problems, the invention ofthe present application provides, in a first aspect, a method ofstabilizing an oxide-semiconductor interface by using a Group Vbelement, which comprises supplying an elemental Group Vb element or twoor more types of Group VB element to the surface of a semiconductor andgrowing an oxide on said Group Vb element, thereby stabilizing theinterface between the oxide and the semiconductor.

Furthermore, the invention of the present application provides, in asecond aspect, a method of stabilizing an oxide-semiconductor interfaceby using a Group Vb element, wherein the semiconductor is silicon, theGroup Vb element is As, and the oxide grown on the Group Vb element is afunctional oxide such as CeO₂, BaTiO₃, PbZrTiO₃, or SrTiO₃.

Additionally, the invention of the present application provides, in athird aspect, a stabilized semiconductor the oxide-semiconductorinterface thereof is stabilized by using a Group Vb element, in whichthe interface between the oxide and the semiconductor is stabilized byan oxide being grown on the surface of the semiconductor with anelemental Group Vb element or two or more types of Group Vb elementbeing incorporated between them.

That is, the inventors of the present application extensively conductedstudies, and, as a result, they have found that, by terminating thesurface of the semiconductor with a Group Vb element, a surfacestructure having extremely low reactivity can be formed at the interfacebetween the oxide and the semiconductor. The present invention has beenaccomplished based on these findings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematically drawn cross section showing an example of asemiconductor formed by a method according to the invention of thepresent application;

FIGS. 2(A) and 2(B) are each a schematically drawn diagram showing thebehavior of atoms in carrying out the method of the invention accordingto the present application;

FIG. 3 in a schematically drawn cross section showing a semiconductorformed by a prior art method;

FIGS. 4 (A)and 4(B) are each a schematically drawn diagram showing thebehavior of atoms in carrying out a conventional method;

FIG. 5 is a high resolution transmission electron micrograph of aCeO₂/Si interface covered with As; it reads that the continuity of thelattice at the CeO₂/Si interface is obtained, and that an acuteinterface is formed;

FIG. 6 is a high resolution transmission electron micrograph of aCeO₂/Si interface not covered with As; the formation of about 10 nmthick amorphous interface layer can be observed at the CeO₂/Siinterface.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a novel method of stabilizing an oxide-semiconductorinterface and a novel type of stabilized semiconductor according to theinvention of the present application are shown, for instance, in FIG. 1.More specifically, a Group Vb element is supplied to the surface of asemiconductor (2) to cover the surface of the semiconductor with acoating layer (3) containing the Group Vb element, and a functionaloxide (1) is grown thereon to stabilize an interface (4) between theoxide and the semiconductor.

In the present invention, the method for supplying the Group Vb elementto the surface of the semiconductor (5) is not particularly limited; forinstance, a molecular beam of the Group Vb element may be supplied tothe surface of the semiconductor after cleaning the surface by heatingthe semiconductor substrate in ultra-high vacuum, so that dimers of theGroup Vb element may constitute the surface.

In the present invention, any semiconductor (1) can be used without anyparticular limitation, and any type of semiconductors may be employed,e.g., the Group IV elements such as silicon, germanium, etc.; the GroupIII-VI compounds such as GaAs, InP, etc.; a hetero semiconductor; apiezo semiconductor; etc.

There is no particular limitation on the Group Vb element for use in thepresent invention, and there may be used elements such as N, P, As, Sb,Bi, etc.

The Group Vb elements enumerated above may be used in the elementalform, but two or more types thereof may be supplied as well.

As a functional oxide (1) to be formed on the coating layer (3) using aGroup Vb element in the present invention, there may be grown adielectric material such as BaTiO₃, SrTiO₃, PbZrTiO₃, etc., or a latticematching oxide such as CeO₂. By using such functional oxides (l), asharply distinguished oxide-semiconductor interface can be implemented.

The method according to the present invention greatly differs from aconventional one in that the oxide-semiconductor interface is stabilizedby covering the surface of the semiconductor with a Group Vb element ata thickness of about 1 atomic layer. Thus, the performance of thefunctional oxide can be sufficiently exhibited yet without losing itsfunction, because an interface layer (reaction layer) is not formedbetween the semiconductor and the interface oxide, but a stableoxide-semiconductor interface is established. Furthermore, as isdescribed hereinafter, a stable oxide-semiconductor interface can beformed independent to temperature.

Conclusively, the invention according to the present invention isapplicable in stably forming capacitors for use in memories of nextgeneration integrated circuits, which, as a result, enables theimplementation of a power-saving high-speed ferroelectric memory devicecapable of realizing high degree of integration, an application to anultra-thin oxide film-semiconductor interface having high dielectricconstant or a gate oxide film, an oxide-semiconductor superlattice and ahigh efficiency light-emitting device.

The stability of the oxide-semiconductor interface according to thepresent invention is described below by referring to its atomicstructure.

Referring to FIG. 2(A), there is shown a surface structure in atomicscale of a (001) surface of a semiconductor, silicon (Si), covered witha Group Vb element, arsenic (As). Dimers of As constitute the outermostsurface of the semiconductor, and the dangling bonds of the dimers arefilled with two electrons. Hence, the reactivity of the surface of As islost. Thus, in the present invention as a result, which is greatlydifferent from the conventional methods of stabilization, no interfacelayer (reaction layer) is formed between the semiconductor and theinterface oxide.

Further referring to FIG. 2(B), the atomic bonding of the As dimers (5)in the outermost layer with the Si atoms (6) in the lower layers is verystrong, and this bonding is formed on the surface as a group of fouratomic bonds. Hence, the resulting surface exhibits less reactivity.This results in a stabilized oxide-semiconductor interface.

Furthermore, the surface stress can be relaxed by forming an As dimerhaving a long bonding length. Thus, the bonding between the As dimersand the Si atoms in the lower layer results with less strain, and thebonding is maintained to higher temperatures independent to thetemperature. This greatly contributes to the stabilization of anoxide-semiconductor interface.

The present invention is described in further detail below by makingreference to Examples.

EXAMPLES

First, a Si (001) substrate, which is used as the semiconductor, washeated in ultrahigh vacuum to form a clean (001) surface. Then, bysupplying a Group Vb element in the form of an As molecular beam on thesurface of the semiconductor, a 2×1 structure of Si (001): Asconstructed from dimers of a Group Vb element, i.e., As, was formed onthe semiconductor substrate. Then, CeO₂ was grown on the thus obtainedsample as a functional oxide at a substrate temperature of 300° C. Forcomparison, CeO₂ was grown on a cleaned surface of Si at the sametemperature.

On observing the interface structure between the semiconductor and thefunctional oxide, as shown in FIG. 5, a continuous lattice was found tobe formed on the CeO₂/Si interface to which the Group Vb element As hadbeen supplied; however, as shown in FIG. 6, the formation of about 10 nmthick reaction layer was observed on the CeO₂/Si interface to which noAs was supplied as the Group Vb element.

From the results above, the surface treatment of silicon by using aGroup Vb element was found to be effective in forming a sharpoxide/silicon interface.

As a matter of course, the present invention is not only limited to theexample above, but various modifications can be made on the details.

As described in detail above, the invention according to the presentapplication provides a method for stabilizing an oxide-semiconductorinterface, which is free from the formation of an interface layer(reactive layer) between a semiconductor and an interface oxide andwhich thereby allows satisfactory exhibition of performance capabilitiesof a functional oxide and achievement of the stability ofoxide-semiconductor interface, yet independent of temperature; it alsoprovides a stabilized semiconductor, and a stabilized semiconductorimplemented by the above method.

Conclusively, the invention according to the present invention isapplicable to the stable formation of capacitors for use in memories ofnext generation integrated circuits, which, as a result, enables theimplementation of a power-saving high-speed ferroelectric memory devicecapable of high degree of integration, an application to an ultra-thinoxide film-semiconductor interface having high dielectric constant or agate oxide film, an oxide-semiconductor superlattice, and a highefficiency light-emitting device.

What is claimed is:
 1. A method of stabilizing an oxide-semiconductorinterface by using a Group Vb element, which comprises supplying anelemental Group Vb element or two or more types of Group Vb element tothe surface of a semiconductor and growing an oxide on said Group Vbelement, thereby stabilizing the interface between the oxide and thesemiconductor.
 2. A stabilizing method as claimed in claim 1, whereinthe semiconductor is silicon, the Group Vb element is As, and the oxidegrown on the Group Vb element is CeO₂, BaTiO₃, PbZrTiO₃, or SrTiO₃.
 3. Astabilized semiconductor the oxide-semiconductor interface thereof isstabilized by using a Group Vb element, in which the interface betweenthe oxide and the semiconductor is stabilized by an oxide being grown onthe surface of the semiconductor with an elemental Group Vb element ortwo or more types of Group Vb element being incorporated between them.